Hi Sebastião,
There are two possibilities I can think of: Your friend is using a bad server and connecting to a different server should solve the problem.
Or your friend's ISP is filtering ed2k-related traffic and your friend has to use Protocol Obfuscation, which is currently not finished in aMule.
kind regards
btw: If your friend is by chance Portuguese (just guessing, as your name seems to be Portuguese), we've a Portuguese section in the forums as well.